Fix build docs script

[jessesquires]

Because of macOS support and adding a Common/ sub-directory, the jazzy build script is broken again.

Same problem as #55 (i.e. realm/jazzy#667). We'll need another workaround, similiar to 7163cf8.

However, this workaround will be significantly more complicated. We need to move the Common/ files to the tmp dir IGListKit/, then we need to move only those files back.

Relevant issues: #235, #328, #270, #53, #368, #365

[Sherlouk]

Can we rely on git? 🤔 Merge all the directories then git reset the source directory leaving just updated docs.

Alternative being we iterate the files, add to an array, move, run jazzy, then move back.

[jessesquires]

Alternative being we iterate the files, add to an array, move, run jazzy, then move back.

We'll have to do this. IG uses mercurial internally.